I was playing Terraria earlier, having just reached the Hell layer (~3000ft.) and after I killed one of those annoying imps, I got a message stating:

You feel an evil presence is watching you.

I read on the official Terraria Online forums that it means the Eye of Cthulhu is about to spawn at the surface. Unfortunately, after receiving the message, I saved the game and quit to look online for that message means (while still in Hell). When I reloaded the game and spawned at the surface, during night-time, Cthulhu wasn't there.

I have more than 10 hearts, which also seems to be a requirement for Cthulhu to spawn and I have not fought any other bosses yet...
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RagnarMay 27 '11 at 8:37

1

Next time, just ALT+ENTER to go in windowed mode and ALT+TAB away which automatically pauses the game if you are in single player. When that message comes a Boolean is made true which is checked in the middle of the night (4,5 minutes in), the reason you don't see him spawn is simply because the state of that Boolean isn't saved...
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Tom WijsmanMay 27 '11 at 23:18

3 Answers
3

It is possible to spawn the Eye of Cthulhu by using a Suspicious Looking Eye.

This item needs to be crafted from 6 lenses. Lenses are occasionally dropped by Demon Eyes (the flying eyes that attack at night along with zombies).

Once you have collected 6 lenses you will need to find a Demon Altar in order to craft the Suspicious Looking Eye. You will probably have to do a bit of searching underground in order to find one of these if you haven't already found one.

Note that in order to summon the Eye of Cthulhu it must be night time. If dawn breaks while fighting the Eye, it will fly away to return the next night with full health.

Thanks! I managed to summon the Eye of Cthulhu and then had my ass promptly handed to me. Managed to beat him, though, and now I have Shadow Armor! WOOO!
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RagnarMay 28 '11 at 8:03

2

I suggest to wait a minute before using Suspicious Looking Eye when the night starts, otherwise you risk that two Eyes of Cthulhu spawn, like it happened to me today. It could be interesting challenge, but be sure to have the right equip.
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DrakeJun 29 '11 at 23:00

While playing, the player may get the message, "You feel an evil presence watching you...", which means that the Eye will awaken soon. After a few minutes the message "The Eye of Cthulhu has awoken!" will appear and the boss will promptly start to attack the player.

In my experience, you'll see the 'watching you' message about 3 times before the Eye of Cthulhu actually spawns. Just keep playing. He'll probably spawn in a couple days game-time.

The Eye should spawn a few minutes after you see the initial message. I've had the message appear 3 times so far and it spawned every time. I don't know if there is a health requirement, but if you are too far underground then the Eye will not spawn. Since you were in Hell at the time when you got the message, that's probably why you didn't it the first time.